Paleoclimatic record of the late Quaternary from a gravity core sediment of Lake Hovsgol in northern Mongolia
Gravity core sediment (HS 7) from Lake Hovsgol(Mongolia) is divided into three sedimentary units on the basis of sediments texture, water contents, occurrence of fossils and sediment color. Unit 1(27¢¦128§̄) is generally massive and is crudely stratified. Ostracods are well preserved over the all interval of Unit1, but diatoms are not well preserved. At Unit2(9¢¦27§̄), mud content is slightly low and lamination is well developed. It is dark greenish gray in the upper part, and dark greenish gray is alternating with light brownish gray in the lower part. Diatom contents increase towards the top and ostracods fragments disappear at the top of Unit 2. Unit3(0¢¦9§̄) is laminated mud in olive gray color. Diatom contents are high but ostracods are not observed in this unit. According to 14C age dating results, we assumed that Unit1 is Pleistocene sediment, Unit2 is sediment of a transitional stage and Unit 3 is Holocene sediment. Chemical composition of trace elements from ostracods show variations through Unit1, especially showing a distinct change at 95¢¦100§̄ interval. It matches to the distribution of ostracod at this interval. Contents of ostracod decrease at the interval and contents of Cytherissa lacustris decrease, but Limnocythere inopinata increase. It was interpreted that warm air was supplied to Lake Hovsgol after LGM(Last Glacial Maximum), causing ice melting. Consequently the bottom environment of Lake Hovsgol experienced some changes as the lake level increased little bit. At the top of Unit 1 appear a lots of pyrite which are arranged in line, and diatoms occure but ostracods are not observed toward the top of Unit 2, and lamination is developed in Unit 2. It means the bottom environment of Lake Hovsgol changed to anoxic condition. At that time, plenty of water was supplied into the lake, resulting in water stratification and cutting off oxygen supply to the bottom of Lake Hovsgol. It made the lake level rise higher, so that the bottom environment changed from oxidation to reduction environment. Finally, the habitation condition of ostracod was destroyed and ostracods couldn't survive there after the end the Pleistocene. This change is more distinctive than that at 95¢¦100§̄ interval. It was probably caused by the effect of decreasing effect of Siberia air mass which was dry and cold, and by increasing warm and humid air mass. So an inflow of warm and humid air mass into the region of Lake Hovsgol incurred ice melting and higher precipitation. It seems that strengthening of East Asian monsoon brought on that climate change. Positive value of ¥ä13C of Unit3 is most of due to the lake water DIC equilibrated with the atmospheric carbon value and increased the photosynthesis after LGM in late Pleistocene.
AGU Fall Meeting Abstracts
- Pub Date:
- December 2007
- 4914 Continental climate records;
- 4926 Glacial;
- 4936 Interglacial